1. Field of the Invention
The present invention relates to an image pickup apparatus and, in particular though not exclusively, to a technique of removing a foreign object from an optical member.
2. Description of the Related Art
An image pickup apparatus that performs imaging by converting an image signal into an electrical signal, such as a digital camera, receives light with an image pickup element (e.g., a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS) device), converts a photoelectric conversion signal output from the image pickup element into image data, and records the image data on a recording medium (e.g., a memory card). In such an image pickup apparatus, an optical low-pass filter or an infrared cut filter is arranged adjacent to a subject with respect to the image pickup element, and when a foreign object (e.g., dust), adheres to a surface of the filter or a cover glass of the image pickup element, the adhering portion is present in a taken image as a black spot. This results in a degraded appearance of the image.
In particular, for a digital single-lens reflex camera with an interchangeable lens, since mechanical operational units, including a shutter, and a quick return mirror, are arranged adjacent to an image pickup element, a foreign object (e.g., dust), produced from the operational units can adhere to the image pickup element or a low-pass filter. Additionally, while the lens is interchanged, dust or other objects can enter a camera body from an opening of a lens mount and adhere to the camera components.
One approach to address this problem that has been suggested is to remove a foreign object (e.g., dust), on a surface of a dustproof curtain that allows a light beam for image taking to pass therethrough arranged adjacent to a subject with respect to the image pickup element by vibrating the dustproof curtain with a piezoelectric element, as discussed in Japanese Patent Laid-Open No. 2003-319222.
According to the technique discussed in this patent document, in order to remove a foreign object on the surface of the dustproof curtain, the dustproof curtain is vibrated by being displaced along the optical axis by the application of a drive voltage to a piezoelectric element connected to the dustproof curtain. However, in order to remove the foreign object from the dustproof curtain, it is necessary to shake the foreign object off the dustproof curtain by application of a force larger than adhesion of the foreign object in the optical axis, and as a result, a large amount of energy is required.
Additionally, according to the above technique, since the dustproof curtain is vibrated by being displaced along the optical axis, if the shape of the dustproof curtain is not circular, it is known that the vibration mode is complicated and vibration efficiency is decreased.
However, an effective imaging area of an image pickup apparatus generally has a rectangular shape with an aspect ratio of 4:3 or 3:2, and therefore, the shape of an effective light beam is rectangular in cross section. In order to allow the effective light beam having a rectangular shape to appropriately pass therethrough, the circular dustproof curtain is large with respect to the effective light beam. Therefore, arranging the circular dustproof curtain within the image pickup apparatus is unfavorable in terms of layout. This produces problems, such as an increase in the size of the image pickup apparatus, an inefficient layout therein.
At the same time, since the above technique requires a special component (namely the dustproof curtain) arranged in the optical axis for image taking, transmittance of the light beam for image taking is reduced, and as a result, the technique is unfavorable in terms of optical function or optical performance, in addition to inefficiency in layout.
Furthermore, a large amount of electric power is necessary for vibration of the dustproof curtain, which has a large size with respect to the effective light beams.